1. The Field of the Invention
This invention relates to light beam detectors and more particularly to that class of apparatus whose mounting needs facilitate locating such devices on any selected height relative to a supporting surface.
2. Description of the Prior Art
The prior art abounds with photoelectric devices utilized for a variety of functions. U.S. Pat. No. 2,626,662 issued on Jan. 27, 1953 to J. E. Coogan teaches an alarm control for clocks and photoelectric switches having an exciter lamp and transmitting lens projecting outwardly from an enclosure to a receiving lens into a photoelectric cell. Audible alarm means are provided within the enclosure operable when the beam is broken as it transits between lenses. An electric alarm clock is housed within the apparatus such that once the alarm is turned to an on condition a solenoid operated rod is caused to close a door in the housing so that tampering with the housing to shut off the alarm clock is prohibited. Any attempt to open the enclosure without breaking the beam, usually placed over the foot of the bed, results in the alarm apparatus being operated thereby forcing the user to get out of bed at the appointed time without simply resetting the alarm and falling off to sleep again.
The U.S. Pat. No. 2,547,332 issued on Apr. 3, 1951 to B. B. Loveless et al describes a race starting apparatus utilizing different audible signals so as to prepare and start the contestants off at the beginning of a race. Included within the apparatus is a photoelectric device which signals that one or more of the athletes participating in the race had crossed the starting line before the transmission of the final starting signal. Such apparatus comprises a light source and a receiver within a housing utilizing a light beam focused into and out of the housing employing individual lenses. A reflecting device is provided in another housing disposed opposite and transverse to the track at the point of which the race is to be started.
U.S. Pat. No. 3,810,148 issued May 7, 1974 to F. W. Karsten et al describes an indicator for detecting and indicating the intrusion or presence of objects on a line or boundary being monitored by officials or monitoring personnel, such as a boundary line at a sporting event or contest. Mr. Karsten's teaching describes a plurality of trained pulse beams of light emanating outwardly from a light transmitting apparatus which in turn is received by a photoelectric cell such that the light beam is interrupted at a periodic controlled rate. Any further interruption, out of phase with the periodicity of interruptions generated by the apparatus comprises a breaking of the beam and hence the crossing of the boundary line which the apparatus monitors.
The aforementioned teachings all suffer the common dificiency of either having an apparatus which is expensive to fabricate or difficult to install, or both. In any event, all of these devices are hard to move from place to place so as to be adjustable easily in installation for a variety of sporting events, including those which require substantial height adjustments.